With further development of offshore oil and gas resources, key areas for oil and gas exploration and development have gradually shifted from land and offshore shallow water areas to far-sea and deepwater areas. On one hand, during oceanic deepwater drilling-in, due to the high-pressure and low-temperature environmental conditions near mudline, it is easy to cause fluid in a pipe string and equipment to form hydrate, thereby blocking the pipe string and preventing the fluid from circulating; on the other hand, due to deepwater depth in the deepwater drilling areas, once the hydrate is formed inside underwater pipe string to cause blockage, it is difficult to de-block the inside of the pipe string to recover in-well circulation. When hydrate blockage occurs in the underwater pipe string and equipment, it will greatly affect the drilling operation efficiency and increase drilling operation cost. For deepwater drilling, main locations where hydrate blockage is extremely easy to form include: one is a riser near an upper end of an underwater wellhead and the other is a riser section cooperating with a lower part of the underwater wellhead, part of the riser section is above mud surface, the other part is below the mud surface.
For on-site deepwater drilling, hydrate formation in an inner passage of the drilling pipe string and equipment is usually inhibited by injecting thermal fluid, kinetic or thermodynamic inhibitors into the well, but the current method can only play a preventive role and can not completely prevent the formation of hydrate in the pipe string and equipment, and cost of the kinetic or thermodynamic inhibitors used on the site is very high, and such additives are not environmentally friendly products and easily pollutes the marine environment, thus causing irreparable damage to the marine ecosystem. After the hydrate has been formed and blocked a circulation channel, there is no effective, economical and environmentally friendly method to remove the blockage. Therefore, it is quite necessary to develop an economical, efficient and environmentally friendly tool to solve the problem of hydrate blockage near the deepwater drilling mudline.
Therefore, based on many years of experience and practice in related industries, the inventor of the present invention provides a riser stub for acoustic resonance decomposition of hydrate in deepwater drilling to overcome the defects of the prior art.